358 On Marine Drerl(jing. 



been denominated " Celtic,'* occupying the intermediate space between 

 the " South b^uropean" and the " Arctic" or Northern. It contains 

 some few species which belong to all the three regions, being found 

 both in Greenland and the Mediterranean ; many Mediterranean 

 species, which appear to reach the northern limit of their range in 

 our seas, and it also furnishes the southern boundary to many arctic 

 forms of animal life. 



Certain of the South European group of mollusca only just reach 

 our coast, not occurring north of the British Channel or the most 

 southern shores of Ireland ; as examples of which, I will mention 

 Lucina pecten, Capsa complanata and castanea ; Cardium aculeatum 

 and tuberculatum ; Gastrochoena pholadia, Calytroea sinensis, Trochus 

 exiguus,Nassa varicosa, Pleurotoma, Striolata, and the southern genus 

 Avicula. Two species which appear to have their greatest develop- 

 ment in the Mediterranean, viz., Cytheriachione and Venus verrucosa, 

 reach their highest latitude on the coast of Carnarvonshire. Several 

 other well-known inhabitants of the Mediterranean extend only along 

 the western shores of the British isles ; being found in the neighbour- 

 hood of Cornwall and Scilly ; again, in the south of Ireland, and round 

 the west coast of that country to the Hebrides and even Zetland. 

 This is the case with Solenecurtus candidus, Psammobia costulata, 

 Lucina spinifera,Cytheriaminuta, Pecten sim il is, Naticasordida, Pleu- 

 rotoma teres, and Erato levis. Tellina balaustina and Arcarariden- 

 tata have only been met with in the west of Ireland and the Isle of 

 Skye. It is worthy of remark that these are mostly old species, all 

 but two being recorded as fossil in the tertiary beds of Sicily, and 

 that they are not found in either the British or St George's Chan- 

 nels ; whether this circumstance is to be regarded as corroborating 

 the opinion that these channels have been formed by the sea at a 

 recent geological period, I would merely suggest for consideration. 

 Two species of neoera, N. costellata and N. abbreviata, inhabiting 

 both the Mediterranean and coasts of Norway, are only known in 

 one British locality, viz.. Loch Fyne, where they were discovered by 

 Professor Forbes and myself in 1846. Of Pecten pes felis, recorded 

 from the Egsean, a single individual, dredged by myself in Loch Fyne, 

 is the only specimen that has been procured alive in our coasts. 



I will now proceed to those marine occupants of the arctic or 

 northern division of the ocean, which apparently reach the southern 

 limit of their range at different points within the area of the British 

 seas. Of these, some only extend to the neighbourhood of Zetland 

 and Orkney; as for example Astarte boreal is, of which I obtained a 

 recent valve off Zetland, and have seen perfect specimens from Spitz - 

 bergen ; of Margarita undata, otherwise only known as a Greenland 

 species, I procured a live specimen near Lerwick. Also Trochus for- 

 mosus, Fusus albus, Certhium nitidum, with a Rostellaria and two 

 species of Fusus obtained last summer, but not yet named or described, 

 are doubtless arctic forms, though as yet only known from the Zetland 



